Process for producing branched olefins from linear olefin/paraffin feed

ABSTRACT

A process for producing branched olefins from a mixed linear olefin/paraffin isomerisation feed comprising linear olefins having at least 7 carbon atoms in 5–50% w comprising in a first stage skeletally isomerising linear olefins in the isomerisation feed and in a second stage separating branched and linear molecules wherein branched molecules are substantially olefinic and linear molecules are olefinic and/or paraffinic; novel stages and combinations thereof; apparatus therefor; use of catalysts and the like therein; and use of branched olefins obtained thereby.

FIELD OF THE INVENTION

The present invention relates to a process for producing branchedolefins from a linear olefin/paraffin feed, and apparatus therefor.

BACKGROUND OF THE INVENTION

The derivatives of long chain olefins having about 7 to 28 carbon atomshave considerable commercial importance in a variety of applications,including detergents, surfactants and freeze point depressants inlubricating oils. Primary derivatives which are used in many householdlaundry detergents include alcohols which are produced byhydroformylation, and alkyl benzenes, for example linear alkyl benzene(LAB) and modified alkylbenzenes (MAB) which are produced by thealkylation of benzene.

In the application to detergents, surfactants and the like, primaryderivatives are generally converted to anionic or non-ionic detergentsor surfactants by sulfonation or ethoxylation, respectively, of thederivative. Important considerations in providing effective detergentsor general surfactants is cold water solubility/detergency, which isusually associated with hydrophobic branched olefin precursors, alongwith the need for good biodegradability which is usually associated withlinear olefin precursors. Since these properties are conflicting it isnot easily possible to provide surfactants, etc. meeting bothrequirements.

U.S. Pat. No. 5,849,960 (Shell Oil Company) discloses an alternativesolution to this problem by providing a new composition of controlledbranching alcohol, and their sulphate derivatives, via the olefinintermediate, in order to decrease hydrophobicity and thereby increasecold water detergency, whilst at the same time exhibiting goodbiodegradability.

The new compositions of U.S. Pat. No. 5,849,960 are prepared using aprocess for producing controlled branching primary alcohols from alinear olefin feed in two stages, via their branched olefins. The olefinfeed is usually a distribution of at least 50 weight % of linear monoolefins in a specified carbon range, the remainder of the feed beingolefin of other carbon number or carbon structure, diolefins, paraffins,aromatics and other impurities, depending on the origin or synthesisprocess used in providing the feed. The location of the double bond isnot limited, the olefin feed composition may comprise alpha-olefins,internal olefins or a mixture thereof. The alkyl branched primaryolefins obtained therefrom have from 7 to 35 carbon atoms, and anaverage number of branches per molecule chain of at least 0.7,containing not only methyl branches but also ethyl branches.

U.S. Pat. No. 6,187,981 (UOP) discloses preparation of modified alkylbenzenes (MAB) and their sulfonates (MABS) by paraffin isomerization anddehydrogenation to olefins, alkylation by olefins of aromatics, andsulfonation. The paraffinic feed for isomerization comprises linear ornormal paraffins having a total of 8 to 28 carbon atoms per molecule,and the isomerised stream for dehydrogenation contains a higherconcentration of lightly branched paraffins.

SUMMARY OF THE INVENTION

In an embodiment, thre is provide a process for producing branchedolefins from a mixed linear olefin/paraffin isomerisation feedcomprising linear olefins having at least 7 carbon atoms in an amount of5–50% w comprising: (a) skeletally isomerising linear olefins in theisomerisation feed thereby producing a reaction product streamcomprising branched molecules and linear molecules; and (b) separatingbranched and linear molecules from at least a portion of the reactionproduct stream wherein branched molecules are substantially olefinic andlinear molecules are olefinic and/or paraffinic.

Further there is provided an apparatus for producing branched olefins bymeans of the process as described above which comprises a first stagecatalytic isomerisation unit, a second stage separation unit and feed,product and optional recycle lines and optionally includes a preliminarystage dehydrogenation unit, and recycle line is to the first stageand/or if present to the preliminary stage unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of selected embodiments of a system forproducing branched olefins from a mixed linear olefin/paraffinisomerisation feed.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, there is provided a process for producing branched olefinsfrom a mixed linear olefin/paraffin isomerisation feed comprising linearolefins having at least 7 carbon atoms in 5–50% w comprising in a firststage skeletally isomerising linear olefins in the isomerisation feed,and in a second stage separating branched and linear molecules whereinbranched molecules are substantially olefinic and linear molecules areolefinic and/or paraffinic. More particularly there is provided aprocess for producing olefins with controlled branching and apparatustherefor.

Preferably the process provides alkyl branched primary olefins having atleast 7 carbon atoms, preferably 7 to 28 carbon atoms, more preferably10 to 16 carbon atoms, and an average number of branches per moleculechain of at least 0.7. Preferably alkyl branches include methyl branchesand also some ethyl branches.

Preferably an isomerisation feed comprises 5% to 50% w, for example 10%to 35% w of substantially linear mono olefins having from 7 to 28 carbonatoms, preferably olefins having from 10 to 16 carbon atoms, with thebalance being paraffins, olefins of other carbon number or carbonstructure, diolefins, aromatics and other impurities, more preferablypredominantly paraffins. Suitable feed comprises streams originatingfrom oil refinery processes such as jet fuel or kerosene, or streamsoriginating from Fischer-Tropsch gas to oil facilities.

Optionally the process comprises in a preliminary stage providing anisomerisation feed by dehydrogenation of a substantially linearparaffinic feed for example comprising less than 10% w olefin, orsubstantially no olefins.

The process may include a recycle from the separation stage to theisomerisation stage or preferably to the preliminary dehydrogenationstage. The recycle may be supplemented by branched olefin/paraffinstreams as by-products of downstream units such as light ends fromhydroformylation of branched olefins comprising predominantly branched(iso)paraffins.

It is a particular advantage of the present invention that the processmay be operated with feed comprising streams from a variety of sourcesincluding an isomerisation or dehydrogenation feed having 0% w to 50% wolefin originating from oil refinery processes or Fischer-Tropsch. Theprocess of the invention provides for selective skeletal branching oflinear olefins whilst paraffins in the feed remain as unreacted linearparaffins, so enabling simple olefin/paraffin separation with use ofknown processes for separation of linear and branched molecules.Excellent selectivity is obtained due to minimal byproduct formation,i.e. minimal cracking products and heavy ends.

Skeletal isomerisation of linear olefins may be carried out by any knownmeans. Preferably skeletal isomerisation is with use of the process ofU.S. Pat. No. 5,849,960, the contents of which are incorporated hereinby reference, with use of a catalytic isomerisation furnace. Preferablyan isomerisation feed as hereinbefore defined is contacted with anisomerisation catalyst comprising a catalyst which is effective forskeletal isomerising a linear olefin composition into an olefincomposition having an average number of branches per molecule chain ofat least 0.7. More preferably the catalyst comprises a zeolite having atleast one channel with a crystallographic free channel diameter rangingfrom greater than 4.2 Angstrom and less than 7 Angstrom, measured atroom temperature, with essentially no channel present which has a freechannel diameter which is greater than 7 Angstrom. Suitable zeolites aredescribed in U.S. Pat. No. 5,510,306, the contents of which areincorporated herein by reference, and are described in the Atlas ofZeolite Structure Types by W. M. Meier and D. H. Olson. Preferredcatalysts include ferrierite, A1PO-31, SAPO-11, SAPO-31, SAPO-41, FU-9,NU-10, NU-23, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, ZSM-57,SUZ-4A, MeAPO-11, MeAPO-31, MeAPO-41, MeAPSO-11, MeAPSO-31, andMeAPSO-41, MeAPSO-46, ELAPO-11, ELAPO-31, ELAPO-41, ELAPSO-11,ELAPSO-31, and ELAPSO-41, laumontite, cancrinite, offretite, hydrogenform of stilbite, the magnesium or calcium form of mordenite andpartheite, and their isotypic structures. Combinations of zeolites canalso be used herein. These combinations can include pellets of mixedzeolites and stacked bed arrangements of catalyst such as, for example,ZSM-22 and/or ZSM-23 over ferrierite, ferrierite over ZSM-22 and/orZSM-23, and ZSM-22 over ZSM-23. The stacked catalysts can be of the sameshape and/or size or of different shape and/or size such as ⅛ inchtrilobes over 1/32 inch cylinders for example. Alternatively naturalzeolites may be altered by ion exchange processes to remove orsubstitute the alkali or alkaline earth metal, thereby introducinglarger channel sizes or reducing larger channel sizes. Such zeolitesinclude natural and synthetic ferrierite (can be orthorhombic ormonoclinic), Sr-D, FU-9 (EP B-55,529), ISI-6 (U.S. Pat. No. 4,578,259),NU-23 (E.P.A.-103,981), ZSM-35 (U.S. Pat. No. 4,016,245) and ZSM-38(U.S. Pat. No. 4,375,573). Most preferably the catalyst is ferrierite.

The skeletal isomerisation catalyst is suitably combined with arefractory oxide as binding material in known manner, for examplenatural clays, such as bentonite, montmorillonite, attapulgite, andkaolin; alumina; silica; silica-alumina; hydrated alumina; titania;zirconia and mixtures thereof. More preferred binders are aluminas, suchas pseudoboehmite, gamma and bayerite aluminas. These binders arereadily available commercially and are used to manufacture alumina-basedcatalysts.

The weight ratio of zeolite to binder material suitably ranges fromabout 10:90 to about 99.5:0.5, preferably from about 75:25 to about99:1, more preferably from about 80:20 to about 98:2 and most preferablyfrom about 85:15 to about 95:5 (anhydrous basis).

Preferably skeletal isomerisation is conducted at elevated temperaturein the range from about 200° C. to about 500° C., more preferably fromabout 250 to about 350° C.

Preferably the isomerisation reaction is conducted at pressure rangingfrom about 0.1 atmospheres (10 kPa) to about 10 atmospheres (1 MPa),more preferably from about 0.5 to about 5 atmospheres (50 to 500 kPa).

The feed to the first stage isomerisation unit comprises linear olefinand more than 50% w paraffin, for example 80–90% w linear paraffin. Itis a particular advantage that the feed is readily available asbyproducts of downstream units or is prepared in a preliminary stagedehydrogenation facility. In a particular advantage the linear paraffinis thought to act as a diluent in the isomerisation process therebyavoiding heavy ends production.

The catalytic isomerisation conditions are preferably relatively mildconditions whereby an amount of unconverted linear olefin is present inthe product stream and is recycled together with linear paraffin,whereby the process may be operated with a high selectivity and lowcracking byproduct production. Suitably up to 30% linear olefin isunconverted and is separated in the second stage process and recycled tothe first stage, more preferably up to 15% w. Preferably theisomerisation is operated in excess of 70% conversion, more preferablyin excess of 85% conversion and most preferably in the range 90 to 95%conversion.

The second stage separation of branched olefins from unreacted feed maybe by any known process. Preferably separation is via branched/linearseparation by contacting the product from the first stage process with asuitable inorganic or organic molecular sieve such as a zeolite ofappropriate pore diameter, preferably a 5A zeolite or urea and the like.

The molecular sieve separates molecules by adsorption, with subsequentdesorption as known in the art. Suitably separation is via a fixed bedcontaining adsorbent as defined with separation of a branched olefinstream and recycle of unreacted linear olefin/paraffin stream.

Suitably separation is conducted at elevated temperature in the range ofabout 100° C. to about 400° C., more preferably from about 180 to about380° C.

Suitably separation is conducted at pressure ranging from about 2 bar(200 kPa) to about 7 bar (700 kPa).

Suitable unit line up and operation may conveniently employ techniquesfor example as known in the MOLEX process (UOP) using Sorbex™separations technology, and a suitable adsorbent may comprisecommercially available ADS-14, ADS-34 used in that technology andequivalent adsorbents.

The separation may use feed pretreatment as known in the art to preventadsorbent poisoning, if required, or this may be achieved in situ inupstream units of the process of the invention.

The preliminary stage dehydrogenation may be by any known means.Preferably dehydrogenation is with use of a standard dehydrogenationfacility employing a Pt catalyst, for example PACOL or with use of adehydrogenation catalyst for example as exemplified in U.S. Pat. Nos.3,274,287; 3,315,007; 3,315,008; 3,745,112; 4,430,517; 4,716,143;4,762,960; 4,786,625; and 4,827,072. However, a preferred catalystcomprises a refractory inorganic oxide having uniformly dispersedthereon at least one platinum group (Group VIII (IUPAC 8–10)) metal andat least one promoter metal, for example as disclosed in U.S. Pat. No.6,187,981. Preferred refractory inorganic oxides include but are notlimited to alpha alumina, theta alumina, cordierite, zirconia, titania,and mixtures thereof. When contacting the catalyst, the dehydrogenationfeed may be in the liquid phase or in a mixed vapour-liquid phase butpreferably is in the vapour phase.

The product stream typically comprises linear olefin in 5–50% w,preferably 10 to 35% w, together with unconverted linear paraffin, andforms the isomerisation feed.

Dehydrogenation conditions include a temperature of generally from about400° C. to about 900° C., preferably from about 400° C. to about 525°C., a pressure of about 1 kPa(g) to about 2000 kPa(g) and a liquidhourly space velocity (LHSV) of from about 0.1 to about 100 hr⁻¹.

Feed to the dehydrogenation unit is optionally provided from an oilrefinery or Fischer-Tropsch process.

Optionally the process may include additional units for separation ofproduct stream from the linear/branched separation unit, fractionatingby molecular weight into for example C₁₀₋₁₄, C₁₅₋₁₆ streams and thelike.

Optionally the process includes additionally the hydroformylation ofproduct olefin with controlled branching by known means to provide thecorresponding alcohol for further conversion to detergents, surfactantsand the like; or alkylation of product olefin with controlled branchingwith benzene by known means to provide the corresponding alkyl benzenes,and optional further sulphonation thereof.

In a further aspect of the invention there is provided a novel processstage or combination thereof as hereinbefore defined.

In a further aspect of the invention there is provided an apparatus forproducing branched olefins by means of the process as hereinbeforedefined. Suitably the apparatus comprises a first stage catalyticisomerisation unit, a second stage separation unit and product andrecycle lines. Optionally the apparatus includes a preliminary stagedehydrogenation unit and recycle line is to the first stage or to thepreliminary stage unit. The apparatus includes a feed stream to thefirst stage unit and/or to the preliminary stage unit.

In a further aspect of the invention there is provided the use ofcatalysts and the like as hereinbefore defined in the process of theinvention as hereinbefore defined.

In a further aspect of the invention there is provided the use of thebranched olefins obtained with the process and apparatus of theinvention for producing detergents, surfactants, freezing pointdepressants in lubricating oils and the like. For use in providingsoaps, detergents and surfactants the branched olefins of the inventionare suitably converted to alcohols by hydroformylation or alkyl benzenesby alkylation and sulphated or ethoxylated by known means.

The invention is now illustrated in non limiting manner with referenceto the figures and examples.

FIG. 1 illustrates a schematic of an apparatus of the invention ashereinbefore defined.

In FIG. 1, isomerisation feed (comprising 5% w to 50% w olefin) is fedto Unit 1 which represents a unit for controlled skeletal isomerisationof olefins. Product stream from Unit 1 is fed to Unit 2 which representsa linear/branched separation unit, for example MOLEX (UOP). This unitproduces two separated streams, a product stream comprising olefin withcontrolled branching which is suitable for hydroformylation to alcoholor alkylation to alkyl benzene and subsequent sulfonation orethoxylation to form commercial detergents, and a recycle streamcomprising linear hydrocarbons, mainly paraffins.

The recycle stream from Unit 2 is fed to Unit A which represents aparaffin dehydrogenation to olefins Unit, for example PACOL (UOP).Product stream from Unit A is recycled to Unit 1.

In the figure the isomerisation feed to Unit 1 is derived from oilrefinery or Fischer-Tropsch, directly or indirectly via PACOL Unit A.Where feed enters depends on its olefinicity, if a feed comprises 0–10%w olefins it enters at Unit A, if it comprises 5–50% w olefins it entersat Unit 1.

The unit line up is optionally fed with dehydrogenation feed fromdownstream Units to Unit A, in addition to isomerisation feed comprising5% w to 50% w olefin to Unit 1.

Unit 1 comprises a catalyst as described in U.S. Pat. No. 5,849,960,Unit 2 comprises a linear/branched separation agent such as urea ormolecular sieve, Unit A comprises platinum dehydrogenation catalyst withor without promoter(s).

The product olefin from Unit 2, having controlled branching is suitablyseparated by molecular weight into streams such as C₁₀₋₁₄, forconversion for example to MLAB type products, C₁₅₋₁₆ which is suitablefor conversion to branched detergent alcohol and the like.

EXAMPLES

Illustrative examples of typical feed and product streams from processesusing the apparatus of FIG. 1 are described in Examples 1 to 3 below andare given in the following Tables 1 to 4.

Example Example 1 Fresh Feed to Isomerisation Unit

In this example fresh feed is passed to isomerisation Unit 1 only (ToU1); product stream is passed to Unit 2 for linear/branched separation(U1/U2); olefin product is obtained from Unit 2 (From U2); unconverted(linear paraffin and any remaining linear olefin) feed is recycled fromUnit 2 to dehydrogenation Unit A (U2/UA); and the resultant linearolefins from Unit A are passed back to Unit 1 for isomerisation (UA/U1).

The olefin product from the Example is shown in column 5 (From U2) andrepresents 100% conversion to branched olefin.

TABLE 1 Model Mass Balance using arbitrary flow units, for case withfresh feed to Unit 1 From To U1 To UA U1/U2 U2 U2/UA UA/U1 Linear olefin30 0 11 0 11 81 Branched olefin 0 0 100 100 0 0 Linear paraffin 70 0 8000 800 730

Example 2 Fresh Feed to Dehydrogenation Unit

In this example fresh feed is passed to dehydrogenation Unit A only (ToUA); product of dehydrogenation Unit A is passed to Unit 1 (UA/U1);product stream of Unit 1 is passed to Unit 2 for linear/branchedseparation (U1/U2); olefin product is obtained from Unit 2 (From U2);unconverted (linear paraffin and any remaining linear olefin) feed isrecycled from Unit 2 to dehydrogenation Unit A (U2/UA); and theresultant linear olefins from Unit A are passed back to Unit 1 forisomerisation (UA/U1).

The olefin product from the Example is shown in column 5 (From U2) andrepresents 100% conversion to branched olefin.

TABLE 2 Model Mass Balance using arbitrary flow units, for case withfresh feed to Unit A To U1 To UA U1/U2 From U2 U2/UA UA/U1 Linear olefin0 0 11 0 11 111 Branched 0 0 100 100 0 0 olefin Linear 0 100 1000 0 10001000 paraffin

Example 3

This example illustrates a method of preparation of a catalyst usefulfor isomerising linear olefins to branched olefins. Anammonium-ferrierite having a molar silica to alumina ratio of 62:1, asurface area of 369 square meters per gram (P/Po=0.03), a soda contentof 480 ppm and n-hexane sorption capacity of 7.3 g per 100 g of zeolitewas used as the starting zeolite.

The catalyst components were mulled using a Lancaster mix muller. Themulled catalyst material was extruded using a 1 inch or a 2.25 inchBonnot pin barrel extruder.

The binder utilized was CATAPAL® D. F4M hydroxypropyl methylcellulosefrom The Dow Chemical Company was used as an extrusion aid. The acidswere obtained from The Aldrich Chemical Company.

Isomerisation Catalyst Preparation

The Lancaster mix muller was loaded with 645 grams ofammonium-ferrierite (5.4% loss on ignition (“LOI”)) and 91 grams ofCATAPAL® D alumina (LOI of 25.7%). The alumina was blended with theferrierite for 5 minutes during which time 152 milliliters of deionizedwater was added. A mixture of 6.8 grams glacial acetic acid, 7.0 gramsof citric acid and 152 milliliters of deionized water was added slowlyto the muller in order to peptize the alumina. The mixture was mulledfor 10 minutes. 0.20 grams of tetraamine palladium nitrate in 153 gramsof deionized water were then added slowly as the mixture was mulled fora period of 15 additional minutes. The extrusion mix had an LOI of43.5%. The 90:10 zeolite/alumina mixture was transferred to the 2.25inch Bonnot extruder and extruded using a stainless steel die plate with1/16″ holes.

The moist extrudate was dried at 125° C. for 16 hours. After drying, theextrudate was longsbroken manually. The extrudate was calcined inflowing air at 200° C. for two hours and at a maximum temperature of500° C. for two hours. The extrudate was allowed to cool in a nitrogenfilled dessicator before loading into the reactors.

Testing Procedure

Isomerisation

A stainless steel tube, 1 inch OD, 0.6 inch ID and 26 inches long wasused as a reactor. A thermowell extended 20 inches from the top of thetube. To load the reactor it was first inverted and a small plug ofglass wool was slid down the reactor tube over the thermowell until ithit the bottom of the tube. Silicon carbide (20 mesh) was added to adepth of about 6 inches. Over this was placed a small plug of glasswool. Approximately 6 grams of catalyst particles, 6–20 mesh admixedwith about 45 grams of fresh silicon carbide (60–80 mesh) were added intwo parts to distribute the catalyst evenly. The catalyst bed wastypically about 10 inches long. Another piece of glass wool was added tothe top of the catalyst and the reactor was topped with 20 mesh siliconcarbide, followed by a final plug of glass wool. A multipointthermocouple was inserted into the thermowell and was positioned suchthat the temperature above, below and at three different places in thecatalyst bed could be monitored. The reactor was inverted and installedin the furnace.

The isomerisation feed utilized was obtained from a Fischer-Tropschreaction of carbon monoxide and hydrogen which yielded a mixture ofprimary linear paraffins and olefins with some minor amounts of dienesand oxygenates present in it. The mixture was fractionated bydistillation into various boiling cuts. The composition of theisomerisation feed used is shown in Table 3 below. The isomerisationfeed was vaporised before contacting the isomerisation catalyst.

To start up the reactor, it was first heated to the desired operatingtemperature over a four hour period and held at the operatingtemperature for 2 hours, all under flowing nitrogen. 60 g/hr ofisomerisation feed was pumped to the reactor. 61/hr of nitrogen was alsopassed over the catalyst with the feed simultaneously. The reactor wasoperated at an outlet pressure of 20 kPa above atmospheric pressure anda temperature of 280° C. Lower temperatures can be used at lower feedrates and if the amount of alcohol present in the feed is lower. Forexample, greater than 90% of the linear olefins are converted tobranched olefins at 230° C. when the oxygenates in the feed are removedfirst from the feed before it is isomerised. Higher temperatures can beused at higher feed rates.

Table 3 below shows the composition of the isomerisation feed used inExample 3, analysed by gas chromatography. Table 4 shows the wt % ofC8–C10 branched olefins, C8–C10 linear olefins and C8–C10 paraffins inthe isomerisation feed (after 0 hours) and in the effluent (after 24 and48 hours of isomerisation).

TABLE 3 Isomerisation Feed Type of hydrocarbon in feed Wt % in feed C7and lighter hydrocarbons 0.12 C8 branched olefins 0.02 C8 linear olefins0.75 1-Octene 0.69 n-Octane 2.21 C9 branched olefins 0.16 C9 linearolefins 8.52 1-Nonene 8.07 n-Nonane 20.03 C10 branched olefins 0.28 C10linear olefins 22.92 1-Decene 20.87 n-Decane 41.12 C11 and heavierhydrocarbons 0.21 C9–C11 alcohols 3.56

TABLE 4 Wt % of C8–C10 branched olefins, C8–C10 linear olefins andC8–C10 paraffins in isomerisation feed (after 0 hours) and in effluent(after 24 and 48 hours) Time on Stream (Hrs) 0 (Feed) 24 Hr. 48 Hr.C8–C10 branched olefins  0.46 (wt %) 33.04 (wt %) 33.16 (wt %) C8–C10linear olefins 32.19 (wt %)  2.52 (wt %)  2.54 (wt %) C8–C10 paraffins63.19 (wt %) 63.32 (wt %) 63.27 (wt %) Branched to linear C8–C10  0.1(wt %)  13.1 (wt %)  13.1 (wt %) olefins ratioThe results in Table 4 show that the majority of linear olefins wereconverted into branched olefins during the isomerisation step. Duringthe isomerisation step a small amount of material boiling below C8 wasgenerated from cracking side reactions. In addition, a portion of theC9–C11 alcohols present in the feed were dehydrated to yield additionalolefins in the product. The average number of alkyl branches on theC8–C10 olefins in the product was 1.0.

1. A process for producing branched olefins from a mixed linearolefin/paraffin isomerisation feed comprising linear olefins having atleast 7 carbon atoms in an amount of 5–50% w consisting of: (a)skeletally isomerising linear olefins in the isomerisation feed therebyproducing a reaction product stream comprising branched molecules andlinear molecules; and (b) separating branched and linear molecules fromat least a portion of the reaction product stream wherein the branchedmolecules are substantially olefinic and the linear molecules areolefinic and/or paraffinic.
 2. The process of claim 1 wherein theisomerisation feed comprises 5% to 50% w of substantially linear monoolefins having from 7 to 28 carbon atoms together with paraffins,olefins of other carbon number or carbon structure, diolefins, aromaticsand other impurities.
 3. The process of claim 1 wherein an isomerisationfeed is contacted with an isomerisation catalyst comprising a catalystwhich is effective for skeletal isomerising a linear olefin compositioninto an olefin composition having an average number of branches permolecule chain of at least 0.7.